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#1
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What Shielded wire to use for RF Test Leads
Looking on the web, I have found numerous suggestions and no definite
answer. To make a shielded test lead for use on a RF device, such as a Signal generator, Oscilloscope, or other, I have seen recommendations for TV coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is best? I know that the TV cable is stiff, with that solid wire in the center, so that would not be the ideal cable to use. It's been years since I used the CB/Ham cable. I know that stuff is stoffer too, but maybe not as bad. As far as handling and softness, I know the Mic cable is probably the best, but I read that it's probably the least desireable because of impedance issues. So what is normally used? BTW: * I might be wrong on those RG numbers. I'm just going on my failing memory. |
#3
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What Shielded wire to use for RF Test Leads
wrote:
Looking on the web, I have found numerous suggestions and no definite answer. To make a shielded test lead for use on a RF device, such as a Signal generator, Oscilloscope, or other, I have seen recommendations for TV coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is best? I know that the TV cable is stiff, with that solid wire in the center, so that would not be the ideal cable to use. It's been years since I used the CB/Ham cable. I know that stuff is stoffer too, but maybe not as bad. As far as handling and softness, I know the Mic cable is probably the best, but I read that it's probably the least desireable because of impedance issues. So what is normally used? BTW: * I might be wrong on those RG numbers. I'm just going on my failing memory. I have used the stranded coax, RG58AU, RG174, Greg |
#4
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What Shielded wire to use for RF Test Leads
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#5
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What Shielded wire to use for RF Test Leads
On Tue, 14 Mar 2017 00:45:43 -0500, wrote:
To make a shielded test lead for use on a RF device, such as a Signal generator, Oscilloscope, or other, I have seen recommendations for TV coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is best? (...) So what is normally used? I use RG-58c/u for 50 ohm test leads. The stranded center wire is more flexible than the rather stiff RG-58a/u. For 75 ohm RF, I use RG-6/u double shielded CATV cable with F connectors on both ends. If I need to plug into test equipment, I have female F to Male BNC adapater. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#6
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What Shielded wire to use for RF Test Leads
On Tue, 14 Mar 2017 09:19:52 -0700, Jeff Liebermann
wrote: On Tue, 14 Mar 2017 00:45:43 -0500, wrote: To make a shielded test lead for use on a RF device, such as a Signal generator, Oscilloscope, or other, I have seen recommendations for TV coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is best? (...) So what is normally used? I use RG-58c/u for 50 ohm test leads. The stranded center wire is more flexible than the rather stiff RG-58a/u. For 75 ohm RF, I use RG-6/u double shielded CATV cable with F connectors on both ends. If I need to plug into test equipment, I have female F to Male BNC adapater. I've never heard of RG58 C/U. Where would someone buy a small amount of it (Online)? Looking on Ebay, I see the A/U type. And that stuff is mostly pre-made cables with either Pl-259 , or BNC connectors on it, OR large rolls of the bulk wire. (25 ft is the shortest). I could buy a 12ft with BNCs, and cut it in half to make two leads, but that's the A/U type. I'm thinking this is something that might need to be ordered from a store that sells Ham Radio stuff, but do they sell small lengths and do they ship it? |
#7
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What Shielded wire to use for RF Test Leads
On Tue, 14 Mar 2017 11:39:39 -0500, wrote:
On Tue, 14 Mar 2017 09:19:52 -0700, Jeff Liebermann wrote: On Tue, 14 Mar 2017 00:45:43 -0500, wrote: To make a shielded test lead for use on a RF device, such as a Signal generator, Oscilloscope, or other, I have seen recommendations for TV coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is best? (...) So what is normally used? I use RG-58c/u for 50 ohm test leads. The stranded center wire is more flexible than the rather stiff RG-58a/u. For 75 ohm RF, I use RG-6/u double shielded CATV cable with F connectors on both ends. If I need to plug into test equipment, I have female F to Male BNC adapater. I've never heard of RG58 C/U. http://www.ebay.com/sch/i.html?_nkw=rg-58c%2Fu Also known as Belden 8262. 30ft for $36 including shipping and BNC connectors on the ends. http://www.ebay.com/itm/191993013419 A little pricey but about what I would expect for a long test lead. It's what's used on test leads and mobile antenna coax cables. Bend the solid center conductor RG-58a/u a few times and it will break. Try to get the type that has both foil and wire braid shields. Where would someone buy a small amount of it (Online)? Looking on Ebay, I see the A/U type. And that stuff is mostly pre-made cables with either Pl-259 , or BNC connectors on it, OR large rolls of the bulk wire. (25 ft is the shortest). I could buy a 12ft with BNCs, and cut it in half to make two leads, but that's the A/U type. Kindly disclose how many feet of the stuff you want and I'll find it for you. How many feet in a "large roll of bulk wire"? eBay is a good place to get short lengths, but not high quality cables. I'm thinking this is something that might need to be ordered from a store that sells Ham Radio stuff, but do they sell small lengths and do they ship it? How many feet and I'll find you a source. It's quite common. Also, you'll need mating BNC, UHF, whatever connectors. I avoid solder type connectors because they like to fall apart. Crimp type are stronger and more reliable. You'll need a crimper: http://802.11junk.com/jeffl/antennas/Misc/slides/crimpers.html 100ft for $42 plus shipping: http://www.l-com.com/coaxial-rg58c-u-bulk-coaxial-cable-stranded-center-conductor-50-ohm-cable -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#8
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What Shielded wire to use for RF Test Leads
Honestly, we havent; the foggiest of what you want to do.
The generator probably has a 50 ohm output. If it's an FM radio, the input is likely 75 ohms. So, you do need a matching transformer. So, there's generally BNC to BNC and an F connector at the receiver. You can buy adapters to adapt the BNC to F. or BNC to quick F. RG-58 isn't terribly inflexible. If you want flexibility, then RG174 should work. At one point, at work we had lots of crimped BNC cables, bought from a reputable manufacturer. Nearly all failed at one point. the broken ones were eventually fitted with clamp BNC plugs. They are not the easiest things to put together, but a resistance soldering tool made it a lot easier. It also depends where you want to put the adapters. |
#9
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What Shielded wire to use for RF Test Leads
On Wed, 15 Mar 2017 07:33:45 -0700 (PDT), "Ron D."
wrote: The generator probably has a 50 ohm output. If it's an FM radio, the input is likely 75 ohms. So, you do need a matching transformer. Nope. Most of my test equipment is 50 ohms. However, I also work with 75 ohm devices and antennas. Transformers do not have a very flat frequency response. If I need a flat frequency response from DC to many GHz, I use a minimum loss pad: https://www.maximintegrated.com/en/app-notes/index.mvp/id/972 https://www.minicircuits.com/WebStore/dashboard.html?model=BMP-5075R%2B https://www.minicircuits.com/pdfs/BMP-5075R+.pdf https://www.pasternack.com/matching-pads-category.aspx http://www.comm-connect.com/8006.html etc... Figure on 5.71dB loss. The technique also works for 50 to 300, 50 to 600 ohms, and other impedances. It also depends where you want to put the adapters. Yep. Coax adapters are fun: http://802.11junk.com/jeffl/antennas/connector-loss/Adapter%20Colluge.jpg Mo http://ham-radio.com/k6sti/match.htm https://www.microwaves101.com/encyclopedias/l-pads#minloss -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#10
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What Shielded wire to use for RF Test Leads
Jeff Liebermann wrote:
On Wed, 15 Mar 2017 07:33:45 -0700 (PDT), "Ron D." wrote: The generator probably has a 50 ohm output. If it's an FM radio, the input is likely 75 ohms. So, you do need a matching transformer. Nope. Most of my test equipment is 50 ohms. However, I also work with 75 ohm devices and antennas. Transformers do not have a very flat frequency response. If I need a flat frequency response from DC to many GHz, I use a minimum loss pad: https://www.maximintegrated.com/en/app-notes/index.mvp/id/972 https://www.minicircuits.com/WebStore/dashboard.html?model=BMP-5075R%2B https://www.minicircuits.com/pdfs/BMP-5075R+.pdf https://www.pasternack.com/matching-pads-category.aspx http://www.comm-connect.com/8006.html etc... Figure on 5.71dB loss. The technique also works for 50 to 300, 50 to 600 ohms, and other impedances. It also depends where you want to put the adapters. Yep. Coax adapters are fun: http://802.11junk.com/jeffl/antennas/connector-loss/Adapter%20Colluge.jpg Mo http://ham-radio.com/k6sti/match.htm https://www.microwaves101.com/encyclopedias/l-pads#minloss I have used some of the six hole ferrite beads to make transformers. six turns, tapped at the fifth turn. The 1.2 turns ratio, squared is a 1.44:1 impedance ratio. These are the same beads used for CATV line taps and broadband splitters. They convert 75 ohms to 52 ohms. I put some into some old Blonder Tongue inline attenuator housings with an F connect on the 75 ohm end and a BNC connector on the 52 ohm end. (52.0833 Ohms) They were handy to use a TV FSM as a 50 ohm RF millivoltmeter. Now, I have some precision attenuators, and a Boonton 9200 RF Millivoltmeter ans different feedthrough terminators.. -- Never **** off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-) |
#11
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What Shielded wire to use for RF Test Leads
Ron D. wrote:
Honestly, we havent; the foggiest of what you want to do. ** The dopey OP has one of these: https://elektrotanya.com/PREVIEWS/38..._sch.pdf_1.png The output Z is anyone's guess. He only wants to use it for old, tube AM radios. IMO use no cable at all, just let it radiate via a length of wire. ..... Phil |
#12
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What Shielded wire to use for RF Test Leads
Jeff Liebermann wrote:
On Tue, 14 Mar 2017 11:39:39 -0500, wrote: On Tue, 14 Mar 2017 09:19:52 -0700, Jeff Liebermann wrote: On Tue, 14 Mar 2017 00:45:43 -0500, wrote: To make a shielded test lead for use on a RF device, such as a Signal generator, Oscilloscope, or other, I have seen recommendations for TV coax (RG59), CB/Ham antenna wire (RG58) and microphone cable. Which is best? (...) So what is normally used? I use RG-58c/u for 50 ohm test leads. The stranded center wire is more flexible than the rather stiff RG-58a/u. A/U is stranded center too. Rg58 is solid. Au cu difference seems to be outer covering difference. Greg For 75 ohm RF, I use RG-6/u double shielded CATV cable with F connectors on both ends. If I need to plug into test equipment, I have female F to Male BNC adapater. I've never heard of RG58 C/U. http://www.ebay.com/sch/i.html?_nkw=rg-58c%2Fu Also known as Belden 8262. 30ft for $36 including shipping and BNC connectors on the ends. http://www.ebay.com/itm/191993013419 A little pricey but about what I would expect for a long test lead. It's what's used on test leads and mobile antenna coax cables. Bend the solid center conductor RG-58a/u a few times and it will break. Try to get the type that has both foil and wire braid shields. Where would someone buy a small amount of it (Online)? Looking on Ebay, I see the A/U type. And that stuff is mostly pre-made cables with either Pl-259 , or BNC connectors on it, OR large rolls of the bulk wire. (25 ft is the shortest). I could buy a 12ft with BNCs, and cut it in half to make two leads, but that's the A/U type. Kindly disclose how many feet of the stuff you want and I'll find it for you. How many feet in a "large roll of bulk wire"? eBay is a good place to get short lengths, but not high quality cables. I'm thinking this is something that might need to be ordered from a store that sells Ham Radio stuff, but do they sell small lengths and do they ship it? How many feet and I'll find you a source. It's quite common. Also, you'll need mating BNC, UHF, whatever connectors. I avoid solder type connectors because they like to fall apart. Crimp type are stronger and more reliable. You'll need a crimper: http://802.11junk.com/jeffl/antennas/Misc/slides/crimpers.html 100ft for $42 plus shipping: http://www.l-com.com/coaxial-rg58c-u-bulk-coaxial-cable-stranded-center-conductor-50-ohm-cable |
#13
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What Shielded wire to use for RF Test Leads
On Thu, 16 Mar 2017 08:19:39 -0000 (UTC), gregz
wrote: Jeff Liebermann wrote: I use RG-58c/u for 50 ohm test leads. The stranded center wire is more flexible than the rather stiff RG-58a/u. A/U is stranded center too. Rg58 is solid. Au cu difference seems to be outer covering difference. Greg Oops, you're right. I stand corrected: RG-58a/u (Belden 8259) http://www.belden.com/techdatas/metric/8259.pdf PVC jacket UL temp temp rating = 75C Attenuation at 1GHz = 70.5dB RG-58c/u (Belden 8262) http://www.belden.com/techdatas/metric/8262.pdf Non-contaminating PVC jacket UL temp temp rating = 85C Attenuation at 1GHz = 74.8dB So, different jackets, higher temperature rating, and less loss for RG-58c/u. Also, RG-58c/u appears to have a military designation (MIL-C-17, M17/155-00001), while RG-58a/u does not. Mo https://abrind.com/faq/ Q: I see different jackets types advertised, what are the differences, and why I should care? A:Jacket Types: PVC-I Polyvinyl Chloride (PVC), black (contaminating). Contaminating jackets will breakdown from sunlight (Ultra-Violet Resistant), and cannot be buried. The PVC-I is rated with a shorter life cycle than PVC-IIA. Suitable for low grade jumpers. PVC-IIA Polyvinyl Chloride (PVC), black (non-contaminating). Non-Contaminating jackets will not breakdown from sunlight (Ultra-Violet Resistant), and suitable for direct burial without conduit. The PVC-IIA is rated with a twenty-year life cycle. The best all-around jacket. (etc...) -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#14
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What Shielded wire to use for RF Test Leads
On Thu, 16 Mar 2017 01:58:16 -0400, "Michael A. Terrell"
wrote: Jeff Liebermann wrote: Nope. Most of my test equipment is 50 ohms. However, I also work with 75 ohm devices and antennas. Transformers do not have a very flat frequency response. If I need a flat frequency response from DC to many GHz, I use a minimum loss pad: https://www.maximintegrated.com/en/app-notes/index.mvp/id/972 (...) I have used some of the six hole ferrite beads to make transformers. six turns, tapped at the fifth turn. The 1.2 turns ratio, squared is a 1.44:1 impedance ratio. These are the same beads used for CATV line taps and broadband splitters. They convert 75 ohms to 52 ohms. I put some into some old Blonder Tongue inline attenuator housings with an F connect on the 75 ohm end and a BNC connector on the 52 ohm end. (52.0833 Ohms) They were handy to use a TV FSM as a 50 ohm RF millivoltmeter. Now, I have some precision attenuators, and a Boonton 9200 RF Millivoltmeter ans different feedthrough terminators.. I initially did the same thing using various iron and ferrite toroid cores. They worked, but not if I wanted a really flat frequency response (+/-0.5dB) over many octaves of frequency range. I had a few adapters that I optimized for frequencies of interest, but getting it fairly flat from 1.5 to 30 MHz (marine bands at about 4.5 octaves) was rather difficult. Instead of fighting the problem, I switched to a minimum loss pad. The low frequency pads ended up inside Pomona aluminum boxes, while the microwave stuff was on microstrip stuffed into a box made from brass or unetched PCB material. Actually, it wasn't quite a minimum loss pad. I worked out the numbers for a 50 to 75 ohm -6.0dB pad instead of -5.71dB, which made power and voltage scaling, measurements, and calculations easier. One problem with minimum loss pads. They develop feet and walk away. I wasted about a day of company time building and characterizing a collection of about 20 attenuators for my own use. Within about 8 weeks, they were all gone, probably "borrowed" by my co-workers. Hint: There's no such thing as a precision attenuator in a lab that works with transmitters. Eventually, they all get cooked. The best I could do was characterize what was left of the attenuator after someone accidentally transmit into it, and compensate for the changes in loss and impedance. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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